Radio communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such communication networks generally support communications for multiple user equipments (UEs) by sharing available network resources. One example of such a network is the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology standardized by the 3rd Generation Partnership Project (3GPP). UMTS includes a definition for a Radio Access Network (RAN), referred to as Universal Terrestrial Radio Access Network (UTRAN). The UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, supports various air interface standards, such as Wideband Code Division Multiple Access (WCDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). The UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks. As the demand for mobile broadband access continues to increase, research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications. For example, UMTS based on WCDMA has been deployed in many places around the world. To ensure that this system remains competitive in the future, 3GPP began a project to define the long-term evolution of UMTS cellular technology. The specifications related to this effort are formally known as Evolved UMTS Terrestrial Radio Access (EUTRA) and Evolved UMTS Terrestrial Radio Access Network (EUTRAN), but are more commonly referred to by the name Long Term Evolution (LTE). The corresponding specifications for the core network side are commonly referred to as System Architecture Evolution (SAE) or Evolved Packet Core (EPC) (where EPC according to the most common definition is a subset of SAE). Together, SAE and LTE/EUTRAN form a complete cellular system referred to as Evolved Packet System (EPS). More detailed descriptions of radio communication networks and systems can be found in literature, such as in Technical Specifications published by, e.g., the 3GPP.
A currently popular vision of the future development of the communication in radio communication networks comprises huge numbers of relatively small autonomous devices, which typically, more or less infrequently (e.g. once per week to once per minute) transmit and receive only small amounts of data (or, alternatively, are polled for data). These devices are not assumed to be associated with humans, but are rather sensors or actuators of different kinds, which communicate with application servers (which configure the devices and receive data from them) within or outside the cellular radio network. Hence, this type of communication is often referred to as machine-to-machine (M2M) communication and the devices may be denoted machine devices (MDs). In the 3GPP standardization, the corresponding alternative terms are machine type communication (MTC) and machine type communication devices (MTC devices), with the latter being a subset of the more general term UE. More detailed descriptions of MTC communication can be found in literature, e.g., in the 3GPP Technical Specification TS 22.368 V. 12.2.0.
With the nature of MTC devices and their assumed typical uses follow that these devices will often have to be energy efficient, since external power supplies will often not be available and since it is neither practically nor economically feasible to frequently replace or recharge their batteries. In some scenarios, the MTC devices may not even be battery powered, but may instead rely on energy harvesting, e.g. gathering energy from the environment, that is, utilizing (the often limited) energy that may be tapped from sun light, temperature gradients, vibrations, etc. For such energy deprived devices, whose traffic is characterized by relatively small and more or less infrequent transactions (often delay tolerant), it may be important to minimize their energy consumption, e.g. between and in combination with the communication events. These devices generally consume energy between the various communication events, e.g. by keeping the radio receiver active to monitor transmissions from the cellular network. Since the periods between the communication events are generally much longer than the actual communication events, this energy consumption may represent a significant part of the overall energy consumption and may even dominate the energy consumption in scenarios where the communication events are infrequent or very infrequent.
During the communication events the actual uplink (UL) transmissions naturally consume significant amounts of energy. This may be magnified by the relatively large control signaling overhead that may be associated with a certain communication event, especially since an infrequently communicating MTC device (or other UE) will go through the idle to connected mode transition prior to every communication event. FIG. 1 shows an exemplary signaling diagram illustrating an example message sequence during the idle to connected mode transition in LTE. As can be seen, the signaling procedure involved during idle to connected mode transition for a UE may be relatively extensive.
A mechanism that has been introduced in radio communication networks in order to save energy in the UEs, e.g. between communication events, is discontinuous reception (DRX), which allows a UE to remain in an energy-saving sleep state most of the time, while waking up to listen for pages in idle mode DRX or downlink (DL) resource assignments (i.e. downlink transmissions) in connected mode DRX at specific occasions as configured by the network. Furthermore, in order to make the DRX mechanism even more effective for energy deprived MTC devices, 3GPP is currently working on extending the maximum DRX cycle length, and thus the sleep period, both for the idle mode DRX cycle and the connected mode DRX cycle. A DRX cycle thus essentially consists of a sleep period followed by an active period and this cycle is repeated over and over again until the device is detached from the network or the DRX configuration is changed. Typically, but not necessarily, the sleep period is longer than the active period. The idle mode DRX cycle, i.e., the paging cycle, is generally configured in the UE through parameters in the system information (SI) that is broadcast in each radio cell, in combination with UE specific parameters in the form of IMSI modulo 1024, and an optional UE specific DRX cycle length. Alternatively, it is also possible to configure a UE specific paging cycle. The connected mode DRX cycle and other DRX parameters (when used) are configured in the UE through optional parameters typically in the RRCConnectionReconfiguration message (RRC is an abbreviation of Radio Resource Control), or later in connected mode. A more detailed description of DRX mechanisms can be found in literature, such as in the reference book 4G LTE/LTE-Advanced for Mobile Broadband by Erik Dahlman, Stefan Parkvall and Johan Sköld, Academic Press, 2011, ISBN:978-0-12-385489-6. As will be appreciated, the DRX mechanisms are defined for both idle mode and connected mode. Generally speaking, these DRX mechanisms are good UE energy saving mechanisms.
However, when the communication events are short and infrequent, each communication event is likely to be preceded by an idle to connected mode transition, and this transition is likely to take a significant portion of time from the whole time needed to perform the data transmission. The potential use of long connected mode DRX cycles may increase the risk of radio link failure during mobility between radio cells, which means that idle to connected mode transition may be triggered many times in such scenarios too. In addition, since the connection setup procedure often involves exchange of a large number of signaling messages, this control plane communication is likely to dominate i.e. comprise more messages, larger data volumes and consume more energy, over the user plane communication. Furthermore, since the signaling procedure involves many nodes in the network as well as significant processing in the network nodes, e.g. in order to set the appropriate configuration parameters, the time intervals separating the messages may be significant. Hence, having the MTC device (or other UE) actively listening for downlink transmissions during the entire idle to connected mode transition, due to the lack of DRX sleep mode possibilities, may cause a relatively high UE energy consumption in some scenarios. In turn, this may have a significant negative impact on the battery lifetime of a UE, e.g. a MTC device.
The U.S. patent application 61/811,961 which was filed on Apr. 15, 2013 by Telefonaktiebolaget LM Ericsson (publ.), introduces a different way of reducing energy consumption of a UE. In one of its aspects, U.S. 61/811,961 introduces the possibility for a user equipment (UE) to apply a temporary DRX cycle during the time period when the UE transitions from an idle mode (e.g. RRC_IDLE) to a connected mode (e.g. RRC_CONNECTED). Applying a temporary DRX cycle in the time period between idle mode and connected mode may provide for several advantages. For example, this may allow the UE to save power during its transition from the idle mode to the connected mode.